1. Field of the Invention
The present invention generally relates to a perforated substrate, and more particularly, to a planar, electrically conductive substrate provided with a multiplicity of perforations. Such a substrate is useful, for example, as a current collector in an electrochemical cell.
2. Prior Art
It is known to form perforated substrates from a sheet of electrically conductive material wherein the perforations are punched or otherwise introduced into the material from one side only. U.S. Pat. No. 4,345,452 to Eberle describes a punching apparatus for forming a strip of lead alloy substrate material into a battery grid. The punching apparatus includes a support for the substrate material to be punched and biased punch members disposed above the supported material for perforating the substrate through one side. The problem is that the resultant burrs formed on the opposite side at each of the perforations introduce stress forces into the substrate that cause it to bow. Conventionally, the bow is removed from the perforated substrate by pressing out the burrs. However, as the width of the substrate becomes greater, the difficulty of compensating for the bow is magnified.
During battery manufacture, it is extremely critical that the substrate current collector is as planar as possible to allow for high speed lamination of the electrode active material onto the substrate. However, it is often difficult to adequately press out the burrs to provide an acceptably planar substrate, and press compensating to remove the bow from a perforated substrate adds an unnecessary step to the manufacturing process. Therefore, there is a need for a perforated substrate of electrically conductive material that conforms to planarity specifications for commercial use, for example, in the commercial production of batteries.